The use of radiation curable resin compositions when producing electronic components or optical components has been increasing in recent years. This is because of high productivity, improvement in the working environment due to the absence of organic solvents, etc.
Against such a background, the radiation curable resin compositions are required to have various physical properties according to the location in which they are used.
For example, in an analog resistive film type transparent touch panel, resin dot spacers are generally used between upper and lower resistive films. When an attempt is made to improve the sensitivity of a touch panel, these dot spacers are desired to have both a lower modulus of elasticity and excellent resilience after deformation at around room temperature. Furthermore, when conductive film wiring is applied to a resistive film such as ITO using silver, etc., and this is covered with a resin for insulation, while taking into consideration improvement of the sensitivity, an insulating covering layer is desired to have a low modulus of elasticity and excellent resilience after deformation.
Here, the dot spacers and the insulating layer preferably have excellent adhesion to a substrate such as a vapor-deposited ITO film or silver.
Furthermore, since the dot spacers and the insulating layer have a detailed shape, they are often applied by printing, but in this case it is necessary for the resin to have an appropriate viscosity.
Among conventional radiation curable resin compositions, resins such as a UV adhesive can give cured materials having a low modulus of elasticity. However, their resilience after deformation is poor, that is, they have a large tan δ in a dynamic viscoelasticity measurement.
However, there are few radiation curable resin compositions that give a cured material having a low modulus of elasticity at around room temperature (storage modulus) and excellent resilience after deformation (low tan δ), and there is no cured material other than a silicone-based material that can give a storage modulus (G′) of 1.2×105 Pa or less and a tan δ of 0.14 or less in a dynamic viscoelasticity measurement (25° C., 1 Hz). However, since the silicone based resin has very poor adhesion to various types of substrates, it is not suitable when adhesion to the substrate is required.
Moreover, even when a radiation curable resin composition containing no silicone-based resin is used, sufficient adhesion cannot be obtained if the substrate is a metal oxide vapor-deposited film having poor wettability, for example, a vapor-deposited ITO film.
That is, the conventional radiation curable resin compositions cannot give a cured material having a storage modulus (G′) of 1.2×105 Pa or less and a tan δ of 0.14 or less in a dynamic viscoelasticity measurement (25° C., 1 Hz), and having excellent adhesion to a vapor-deposited ITO film.